This project focuses on the mechanism of reactions of systems requiring adenosyl-cobalamin (coenzyme B12) specifically propanediol dehydrase. Experiments of three kinds are being carried out (1) kinetic and product studies using substrate analogues, such as glycerol, including observation of kinetic isotope effects and stereochemistry of specifically deuterated derivatives (2) esr experimentation of reacting systems for detection ad characterization of possible radical-type intermediates and (3) attempts to isolate cobalamin-substrate or enzyme-substrate intermediates. Catalytic studies of serine proteases are aimed at observation and characterization of the tetrahedral intermediate and the question of concertedness of proton transfers within the catalytic triad during its formation and decomposition. BIBLIOGRAPHIC REFERENCES: R.G. Eagar, Jr., W.W. Bachovchin, and John H. Richards, Mechanism of Action of Adenosylcobalamin: 3-Fluoro-1,2-propanediol as Substrate for Propanediol Dehydrase-Mechanistic Implications, Biochemistry, 14, 5523, 1975. M.W. Hunkapiller, M.D. Forgac, and John H. Richards, Mechanism of Action of Serine Proteases: Tetrahedral Intermediate and Concerted Proton Transfer, Biochemistry, in press (1976).